1. Field of the Invention
The present invention relates to a solid state imaging device, and more particularly to a solid state imaging device suitable to produce a color image signal.
2. Description of the Prior Art
In the prior art, when a color image signal with three or more color signals is to be produced by one or two solid state imaging devices, image sensing parts of the imaging devices receive light through color separating optical members such as color filters arranged in stripe or mosaic to form electrical information representative of the respective colors in picture cells and the electrical information of the picture cells are time-serially read out through a common transfer path.
FIG. 1 shows an example of a well-known prior art solid state imaging device which utilizes a frame transfer (FT) type charge coupled device (CCD).
In FIG. 1, numeral 1 denotes an image sensing part having a plurality of photo-electric converting picture cells arranged in rows and columns. Numeral 2 denotes a memory part for storing charge information of the picture cells of thee image sensing part 1. Numeral 3 denotes a horizontal register which functions as a read transfer path. It reads out the information of the memory part 2 one horizontal line at a time and transfers the line information horizontally to time-serially produce point-sequential signals.
By arranging color separating stripe color filters as shown in FIG. 2 in front of the imaging part 1 with the pitch of the color filters R (red), G (green) and B (blue) being coincident with the pitch of the picture cells of the image sensing part 1, the picture cells in the respective columns produce signals representative of the respective colors and the point-sequential color signals are time-serially produced from the horizontal shift register 3.
The color signals thus produced are converted to, for example, an NTSC signal by a signal processing circuit as shown in FIG. 3.
The point-sequential image output signals from a CCD amplifier 4 are sampled and held by a signal separation circuit 8 comprising three sample-and-hold circuits 5, 6 and 7 so that a red signal E.sub.R, a green signal E.sub.G and a blue signal E.sub.B are separated. The color signals E.sub.R, E.sub.G and E.sub.B are level-adjusted by variable gain amplifiers 9, 10 and 11, respectively, so that a white balance is controlled. The level-adjusted color signals are than processed by processing circuits 12, 13 and 14 each including a clamp circuit, a .gamma. correction circuit and an aperture correction circuit, and the signals are converted to a luminance signal and two color difference signals by a matrix circuit 15, and they are converted to the NTSC signal by an encoder 16.
With such an arrangement, the horizontal register 3 sequentially reads out three primary colors. In order to read them with a carrier of 3.58 MHz, a clock of 3.58 MHz.times.3=10.74 MHz is required. However, as the clock frequency is high, the transfer efficiency is reduced and the power consumption increases. As a result, a problem is encountered when the number of picture cells of the horizontal shift register or the number of horizontal picture cells of the image sensing part 1 is large.